Pulse power supply for regenerating magnetic energy

ABSTRACT

In order to provide a pulse power supply device using regenerating magnetic energy stored in a discharge circuit to a capacitor so as to use it as next discharge energy and supplying a bipolar pulse current with high repetition, a bridge circuit is composed of four inverse-conductive semiconductor switches, a charged energy source capacitor is connected to a DC terminal of the bridge circuit, and an inductive load is connected to its AC terminal. A control signal is supplied to gates of the inverse-conductive semiconductor switches, and a control is made so that when a discharge current rises, is maintained or is reduced, all the gates are turned off, and the magnetic energy of the electric current can be automatically regenerated to the energy source capacitor by a diode function of the switches. Further, a large-current power supply is inserted into a discharge circuit so as to replenish energy loss due to discharge, thereby enabling high-repetition discharge.

TECHNICAL FIELD

The present invention relates to a pulse power supply device forsupplying pulse current to an inductive load.

BACKGROUND ART

When a large electric current is supplied to an inductive load, pulsepower supply devices, in which normally an energy source capacitorcharged with high voltage is connected to the load by using switchessuch as an ignitron, a discharge gap switch and a thyristor so that acapacitor discharge is started, are generally used.

In these discharge switches, diodes called clamp circuits are generallyconnected to loads in parallel or to capacitors in parallel. After theelectric current becomes maximum, a capacitor voltage is inverted andsimultaneously the diodes are turned on, and the load current reflows tothe diodes. As a result, reverse charging of the capacitor is prevented,and the clamped electric current continuously flows while beingattenuated with time constant L/R due to electric resistance of theload.

On the other hand, in the applications of the pulse current, frequentlyrise time is more important than an attenuated waveform. Pulsehigh-magnetic field bending magnets of compact medical synchrotronaccelerators and the like do not use the maximum magnetic field butrequire an operation such that the magnetic field is raised with time.For this reason, it is demanded that the electric current is attenuatedquickly and a pulse rate is heightened. Further, gas excitation laserpower supply requires high speed rise of a voltage and high repetition,and thus high repetition control is required as discharge power supply.

In order that the rise of the discharge current is stopped bycontrolling switches when the discharge current reaches a necessarycurrent value, switches are switched from those only for ON control suchas an ignitron, a discharge gap switch and a thyristor to semiconductorswitches having self arc-suppressing ability using a gate signal such asa GTO thyristor and an IGBT (Insulated-gate Bipolar Transistor).

An inductive current on the load side, however, is clamped at a voltageof 0, and is only attenuated by the diodes at long time constant L/R ina freewheeling state. The energy is wasted and time to wait for theattenuation is required, thereby raising a technical problem of thepulse power supply devices requiring increased capacity and highrepetition.

When the electric current in the freewheeling state is cut off and itsmagnetic energy can be regenerated to the capacitor, the wasted energyis reduced and further the energy returned to the capacitor isregenerated as next-time energy, so the pulse current generating powersupply which has high energy efficiency and high repetition can berealized.

DISCLOSURE OF THE INVENTION

FIG. 2 is a diagram explaining a basic operation of the presentinvention. A power supply side has a constitution of a current switch ofa snubber energy regenerating system. A capacitor which temporarilystores snubber energy corresponds to an energy source capacitor of thepresent invention. The current switch of the snubber energy regeneratingsystem is disclosed in Japanese Patent Application Laid-Open No.2000-358359 “FORWARD AND BACKWARD DIRECTION CURRENT SWITCH FORREGENERATING SNUBBER ENERGY” (Patent Document 1). The present inventionutilizes the constitution of the above-mentioned current switch forregenerating the snubber energy, but the Patent Document 1 describes thecurrent switch for temporarily storing magnetic energy of a breakingcurrent circuit into a snubber capacitor and discharging it into a loadat the time of next energizing. On the contrary, the present inventionis different from the invention in the Patent Document 1 in that theenergy source capacitor is charged with full energy, and the load isdriven only by the energy, and further, when the pulse is ended, themagnetic energy remaining in the load is regenerated to the energysource capacitor.

In an example of FIG. 2, a load is an inductive load and is representedby a resistor R and an inductance L. In the case of gas laser, however,the load is a discharge electrode, and in the case of an acceleratorbending magnet, the load is a dipole coil which is transformer-coupled.In both cases, the load is regarded as a load where L and R areconnected in series. When the time of a discharge pulse is sufficientlyshorter than the time constant L/R, the energy is mostly supplied bymagnetic energy of the inductance.

An operating sequence of FIG. 2 is explained with reference to FIG. 3.Firstly a capacitor 1 is charged so as to have polarity of FIG. 2 (acharging circuit is not shown), and when switches S1 and S2 are turnedon, electric charges of the capacitor start to flow to the load. When anelectric current becomes maximum and the voltage of the capacitor isnegative (forward-direction voltage of a diode), the load current reflows via the diode and is brought into a freewheeling state, and theload current continues to flow in two parallel lines in a directionwhere “a path where a main current flows” is written. Thecharacteristics of the switch constitution and the operation are thatthe electric current in the freewheeling state continuously flows in twoparallel lines. As a result, a current carrying capacity of the switchesis only half, and thus this example is economical.

When the switches S1 and S2 are turned off, the electric current in thefreewheeling state is cut off, and the capacitor 1 is recharged into thesame polarity via two diodes. As a result, the electric current isquickly reduced and when it becomes zero, the diodes prevent reversecurrent, thereby stopping the electric current.

After the switches S1 and S2 are turned on, when any one of the switchesS1 and S2 is turned off while the capacitor voltage remains, the loadcurrent is brought into the freewheeling state, and the capacitorvoltage is maintained. When the switch is turned on again, the electriccurrent restarts to rise. The high-speed on/off operation of theswitches possibly enables PWM control of the capacitor dischargecurrent. This function cannot be realized by the simple current switchesof the snubber regenerating system.

When the switches and the diodes in the constitution of FIG. 2 are used,discharge can be started, maintained and reduced by turning on/off theswitches at arbitrary timing. Further, the magnetic energy with the samepolarity is regenerated to the capacitor.

FIG. 4 is a principle diagram for developing the present invention inboth directions of the electric current.

A difference of this drawing from FIG. 2 is that four units where diodesand switches are connected in parallel are installed in inverse-seriesand in inverse-parallel as shown in FIG. 4, so that a bidirectionalelectric current is allowed to flow in the load. The same point is thatwhen the switches are turned off, the magnetic energy is regenerated tothe capacitor 1 (as in FIG. 2, the charging circuit is not shown).

In order to change the direction of the electric current to the load,selection from an operating switch group is brought into a “crossstate”, namely, the switches S1 and S2 are turned on in a currentforward direction and the switches S3 and S4 are turned on in a currentbackward direction. “A pair of the switches are selected in the crossstate” means that when the four switches are arranged into aquadrangular shape, two of them positioned on a diagonal line areselected. A rational design is made preferably in a manner that theswitches and capacities of the diodes according to a level of themaximum electric current in the forward and backward directions areselected.

FIG. 5 is a diagram illustrating a simulation circuit showing that theenergy source capacitor 1 can be replenished with energy by alow-voltage large-current power supply 5 inserted into the dischargecircuit, and a waveform as its result. According to the waveform of FIG.5, the capacitor voltage and the load current rise according to thenumber of discharges, but this is because when a voltage which is notless than a voltage of a DC resistance is injected from an externalpower supply, the discharge current rises. When the voltage of theexternal power supply is increased or decreased in such a manner, thevalue of the pulse current can be controlled.

Prior to the operation, when a voltage is applied to a circuit by thelow-voltage large-current power supply 5, an electric current which isdetermined by a resistor flows. Since the magnetic energy is regeneratedto the capacitor 1 and the capacitor 1 is charged by cutting off theelectric current using a current switch, the pulse current forhigh-speed boot can be obtained only by the low-voltage power supplywithout preparing a high-voltage power supply for charging thecapacitor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram explaining an embodiment of the present invention;

FIG. 2 is a diagram explaining a basic principle of the presentinvention;

FIG. 3 is a diagram explaining a sequence of an electric current, avoltage and switches in FIG. 2;

FIG. 4 is a diagram explaining a basic principle of bidirectionalcurrent of the present invention; and

FIG. 5 is a model diagram of a calculator simulation for analyzing abasic principle of a method of supporting a capacitor voltage, and asimulation waveform of a load current and the capacitor voltage of thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a circuit diagram illustrating an embodiment of the presentinvention. A difference of FIG. 1 from FIG. 4 is that when anaccelerator bending magnet 6 as a concrete example of a load is excitedby a pulse current via a current transformer 3, four power MOSFETs areconnected in inverse-series and in inverse-parallel. As a result, thefour power MOSFETs compose a bridge circuit.

It is assumed that power MOSFETs used here are made of silicon carbide(SiC), and are quickly turned on/off with high withstand voltage, haveless conducting loss, and can effectively utilize body diodes (alsocalled parasitic diodes) as a substitution of parallel diodes.

Even when present power MOSFETs made of silicon which cannot practicallyuse body diodes are used, they can be used by forcibly bringing theminto an ON state by means of gate control when they are in an inverseconducting state. An inverse conductive type GTO thyristor or a unit inwhich diodes are connected to semiconductor switches such as IGBT andthe like in parallel can produce the effect of the present invention.

In the present invention, a switch, which prevents an electric currentfrom flowing in a forward direction when the switches are off butconducts in a backward direction, is called an inverse-conductive typesemiconductor switch. Its examples are the power MOSFET, theinverse-conductive type GTO thyristor, and the unit in which the diodesare connected to the semiconductor switches such as IGBT and the like inparallel.

A gate signal is supplied to the power MOSFET switches G1 to G4 from acontrol device 7 shown in FIG. 1. A pair of the switches G1 and G2 areselected “in a cross state” so that a direction of the electric currentis a forward direction, and when a pair of the switches G3 and G4 areselected, the direction of the electric current is the backwarddirection. This is necessary for enabling a flow of a magnetizationreset current for improving an exciting property of a currenttransformer for pulse operation of a compact medical accelerator bendingmagnet.

In FIG. 1, a low-voltage large-current power supply 5 is insertedbetween an inductive load 6 and the switch 2, and when its voltage isapplied to a discharge current in series, energy can be replenished atevery discharge. Further, at the first time, the low-voltagelarge-current power supply 5 allows an electric current 4 in thecircuit, and by cutting off the electric current 4 by the current switch2, the capacitor 1 can be charged like a snubber capacitor, and thus apulse current for high-speed boot can be obtained only by thelow-voltage power supply without preparing a separate high-voltage powersupply for charging the capacitor. Needless to say, a general method ofconnecting a charging power supply to the capacitor 1 so as to chargethe capacitor is effective.

INDUSTRIAL APPLICABILITY

According to the present invention, the gate signals of bidirectionalcurrent switches having a bridge constitution composed of foursemiconductor switches connected to diodes in parallel as the switch ofthe energy source capacitor for generating an electric current arecontrolled, so that the electric current to the inductive load can bestarted, maintained and stopped at a high speed. At this time, when theelectric current is reduced, the magnetic energy is regenerated with thesame polarity as that of the capacitor. As shown in FIG. 5, when thelow-voltage large-current power supply 5 is inserted into the currentcircuit, the charging voltage of the capacitor can be increased ordecreased while a discharge cycle is being repeated.

When the two power MOSFETs in series have the withstand voltage, a totalcapacity of the four switch elements may be basically half, and furtherwhen it is considered that a pulse conductive current flows in two armsin parallel, the total capacity is half. For this reason, the presentinvention can be applied basically without increasing voltage-currentcapacity in comparison with conventional pulse power supply.

1. A pulse power supply device for supplying a bipolar pulse current toan inductive load with high repetition and regenerating residualmagnetic energy of a system so as to use it for next discharge, whereinan energy source capacitor initially charged is connected to a DCterminal of a bridge circuit composed of four inverse-conductivesemiconductor switches, and the inductive load is connected to its ACterminal, a control circuit for giving a control signal to gates of theinverse-conductive semiconductor switches and controlling an on/offstate of the semiconductor switches is further provided, the controlcircuit controls pairs of the four inverse-conductive semiconductorswitches composing the bridge circuit positioned on diagonal lines,respectively, so that the pairs are turned on simultaneously oralternately, and controls the pairs so that when at least one of thepaired two inverse-conductive semiconductor switches is on, the otherpaired inverse-conductive semiconductor switches are off.
 2. The pulsepower supply device using regenerating magnetic energy according toclaim 1, wherein a low-voltage large-current power supply is inserted inseries with the inductive load so as to replenish lost energy due todischarge so as to increase or decrease next discharge current.
 3. Thepulse power supply device using regenerating magnetic energy accordingto claim 1, wherein the inverse-conductive semiconductor switches areany one kind of power MOSFETs, inverse-conductive GTO thyristors andunits constituted so that diodes and semiconductor switches such as IGBTand the like are connected in parallel.
 4. The pulse power supply deviceusing regenerating magnetic energy according to claims 1, wherein one ofthe two pairs of inverse-conductive semiconductor switches is replacedby diodes.
 5. The pulse power supply device using regenerating magneticenergy according to claim 2, wherein the inverse-conductivesemiconductor switches are any one kind of power MOSFETs,inverse-conductive GTO thyristors and units constituted so that diodesand semiconductor switches such as IGBT and the like are connected inparallel.
 6. The pulse power supply device using regenerating magneticenergy according to 2, wherein one of the two pairs ofinverse-conductive semiconductor switches is replaced by diodes.
 7. Thepulse power supply device using regenerating magnetic energy accordingto 3, wherein one of the two pairs of inverse-conductive semiconductorswitches is replaced by diodes.